1. Field of the Invention
The present invention relates to a process for washing a powdery and/or granular resin and a washing device for use in the process therefor and, more particularly, to the process for washing the powdery and/or granular resin and the washing device for use in the process therefor, which are highly efficient in washing, which require simplified equipment, and which are less expensive in running cost.
2. Description of Related Art
Such a powdery and/or granular resin as being produced by polymerization processes generally contains components of low molecular weights, by-products, residues of catalysts and polymerization promoters, and solvents. In molding or forming it as it is, the powdery and/or granular resin presents drawbacks that it corrodes equipment to be used and it imparts a color. And the powdery and/or granular resin itself may suffer from the disadvantages that its properties deteriorate with a lapse of the time period and it generates bubbles upon molding. Further, when the resin containing impurities is used as a material for electrical and electronic instruments, they may cause even an error in operation. Thus, it is required that such impurities should be removed as much as possible.
Therefore, a variety of processes of washing out such impurities from the powdery and/or granular resin has heretofore been developed and applied in order to satisfy requirements for removing the impurities therefrom, however, they have problems in common that they are low in washing efficiency.
For instance, polyphenylene sulfide (PPS) in a form of powder, synthesized by polymerization, has unreacted p-dichlorobenzene (PDCB), N-methylpyrrolidone (NMP) as a solvent, sodium chloride as a by-product, a polymerization promoter, oligomers and so on adhered. Conventional processes for removing those impurities involve stirring the PPS, together with a washing liquid, by using a washing vessel with a stirring blade. The conventional processes, however, suffer from the disadvantage that the impurities cannot be removed to a sufficient extent, thereby placing the limit to an improvement in purity of the resin. They also have the problems that washing operation should be repeated plural times, i.e., three to ten times, when the products are washed in a batch system, and a plurality of washing vessels, i.e., three to ten washing vessels, should be provided when the products are washed in a continuous system using a complete mixer. Hence, those processes render equipment complicated, require expensive investment costs and causes an increase in an amount of a washing liquid to be consumed and an amount of waste to be treated as well as an increase in power for stirring, resulting in a rise of running costs.
It is also known of a process for continuously treating a slurry of the PPS with hot water by means of an indirect heat exchange, as disclosed in Japanese Patent Unexamined Publication (kokai) No. 49,233/1984. This process serves as simplifying equipment and shortening a time period for treatment, however, it has washing efficiency as low as the conventional ones in a batch system.
Further, U.S. Pat. No. 4,526,684 discloses a process which allows a slurry of the PPS to flow in a treating vessel and a washing liquid to pass through a filter mounted around the treating vessel. This process also has the drawbacks that its efficiency in washing is low, the filter clogs, and equipment is made so complicated to require a complex operation.